The attack was carried out shortly after 'iftar', the meal that ends the daily fast in the holy month of Ramzan. A news channel quoted intelligence sources as saying that at least four terrorists, wearing suicide vests and carrying automatic weapons, were involved in the attack.

One attacker rammed an explosives-laden vehicle into the wall of the Inter-Services Intelligence office at Barrage Colony in Sukkur, Sindh's third largest city located 500 km from the financial hub of Karachi.

The others stormed into the regional headquarters of the ISI, lobbed grenades and exchanged fire with personnel inside. Two attackers blew themselves up inside the building while another was captured, the news channel reported.

At least five persons were killed and 38 others, including women and children, injured in the attack, officials said.

Witnesses said they had heard at least four blasts within the high-security compound that houses the ISI office and residences of intelligence, police and civil officials.